1. Technical Field
The present invention is related to a method of cleaning watery i.e. humid ventilation air containing liquids which have been gasified during cooling or lubrication of converting machines. The method comprises cooling of the ventilating air in one or several steps to a temperature below the condensing point of the gasified substances in the ventilating air, so that said substances condense, and collecting the condensed liquids. The invention is also related to an apparatus for carrying out the method and is preferably intended for use in oil-cooled rolling mills or other oil- or liquid-cooled converting machines.
2. Background Art
In rolling mills, the rollers coming into contact with the ingots or metal billets to be rolled have to be forcefully cooled. This cooling is normally carried out by spraying an oil-based liquid over the rollers. During the cooling, large quantities of oil will be gasified and absorbed by the ambient air. For environmental reasons, this air has to be cleaned before it is released to the atmosphere or reused. The air quantities can be very large, e.g. of the order of 50,000 m.sup.3 /h.
The polluted air periodically contains, in addition to oil, large quantities of water due to changes in atmospheric humidity. When cleaning the air by conventional cooling in order to condense the gasified oil, large quantities of water will also condense e.g. of the order of 40 m.sup.3 per 24 hours at 100,000 m.sup.3 /h, as the air has to be cooled to a comparatively low temperature to obtain a sufficient cleaning of the air. While a large portion of the condensed oil can be separated from the water comparatively easily and reused, a certain quantity of condensed oil will remain in the condensed water. It is very time consuming and expensive to separate the oil completely from the water. The quantity of oil remaining in the water after an economically justified separation of oil and water is so large that the water should not be released to a municipal facility without further cleaning. The cleaning of ventilating air containing oil and water thus presents a problem that is difficult to solve in an economically satisfactory way due to the large quantities of water containing oil that are obtained.